Role of zeolite properties in bio-oil deoxygenation and hydrocarbons production by catalytic cracking

Abstract

A comparison between the behavior of Y and ZSM-5 zeolites having the same Si/Al ratio was established in the catalytic cracking of bio-oil for producing fuels and platform chemicals. The catalysts were prepared by agglomerating each zeolite with a mesoporous γ-Al2O3 matrix. Properties of the zeolites and the catalysts were characterized by N2 ads/desorption, SEM-EDX, pyridine-FTIR, tBA-TPD, and NH3-TPD techniques. The experiments were conducted in a continuous two-step catalytic cracking system (TS-CC) at 450 °C. Both catalysts are highly selective to C5-C12 hydrocarbons, with a composition strongly affected by the porous structure and acidity of the zeolite. The HZSM-5 catalyst (high acid strength and Brønsted/Lewis ratio) promotes cracking and deoxygenation reactions that lead to C2−C4 olefins which condensate into aromatics, yielding 9% of 1-ring aromatics (3% BTX) and 4% of naphthalenes for a feed conversion of 85%. These reactions are less favored over the HY catalyst, which promotes olefins oligomerization and hydrogen-transfer reactions, yielding 14% of highly aliphatic gasoline (> 30% linear paraffins) and 5% of C13−C20 diesel fraction (> 90% long chain paraffins). The remaining upgraded bio-oil obtained with both catalysts is composed of light oxygenates, with ketones, acids and esters as main components and low concentration of phenolic compounds.